Mantle Heat Exchangers Research Articles

TRNSYS model of a thermosiphon solar domestic water heater with a horizontal store and mantle heat exchanger

A new TRNSYS model of a solar domestic water heater is presented. It describes a thermosiphon system with a horizontal store and a mantle heat exchanger. The fluid inlet is placed at the top of the annular gap. This new TRNSYS ‘Type’ is developed from the standard Types 45 and 38, with some new features. Results of the new type are compared with two sets of experimental data. The new model is in accordance with experimental data, comparing daily energy delivered and draw-off temperature profiles.

Heat transfer correlations for vertical mantle heat exchangers

This paper investigates heat transfer in vertical mantle heat exchangers for application in low flow solar domestic hot water systems. Two new heat transfer correlations for vertical mantle heat exchangers with top entry port and bottom exit ports are developed. The correlations are based on computational fluid dynamic modelling of whole vertical mantle tanks. The correlations are combined with a heat storage model in a simulation program that predicts the yearly thermal performance of low flow solar domestic hot water systems based on mantle tanks. The model predictions of energy gains and temperatures are compared with outdoor measurements and the model is found to give reliable results.

Mixed convection in a narrow rectangular cavity with bottom inlet and outlet

Abstract A model describing the heat transfer in horizontal mantle heat exchangers used in solar water heaters has been developed by approximating a narrow horizontal annulus to an equivalent rectangular cavity. Particle tracking velocimetry (PTV) and computational fluid dynamics (CFD) simulations were used to determine the flow field. The flow is in the mixed-convection regime, where buoyancy locally affects the flow field and heat flux. The effect of the heat-transfer wall temperature distribution on the net heat-transfer rate has been quantified by the introduction of a stratification correction parameter. A mean Nusselt number, defined by using the difference between the inlet temperature and mean heat-transfer wall temperature, is shown to be independent of buoyancy forces when the stratification correction parameter is taken into account. A correlation has been developed for the mean Nusselt number for a range of geometries and boundary conditions. This correlation predicts the net heat-transfer rate to within 10%.

Mantle heat exchangers for horizontal tank thermosyphon solar water heaters

Mantle heat exchangers for horizontal tank thermosyphon solar water heaters

Characteristics of vertical mantle heat exchangers for solar water heaters

Characteristics of vertical mantle heat exchangers for solar water heaters

00/00383 On the verification of one dimensional heat flow in a horizontal thermosyphon storage tank

The characteristics of horizontal mantle heat exchangers are investigated for application in thermosyphon solar water heaters. An experimental model of a horizontal mantle heat exchanger was used to evaluate the flow patterns in the annular passageways and the heat transfer into the inner tank. Flow visualisation was used to investigate the flow structure, and the heat transfer was measured for isothermal inner tank conditions. A numerical model of the flow and heat transfer in the annular passageway was developed and used to evaluate the heat flux distribution over the surface of the inner tank. The numerical results indicate that configurations of mantle heat exchangers used in current solar water heater applications degrade thermal stratification in the inner tank. The effects of inlet flow rate, temperature and connecting port location are quantified.

00/00495 Some aspects concerning modelling the flow and heat transfer in horizontal mantle heat exchangers in solar water heaters

Low driving forces in thermosyphon solar water heaters make the measurement of thermosyphonic flow difficult. Tests were made on a thermosyphon solar water heater to monitor the flow-rate using a hydrogen bubble flow meter. An analytical equation for the flow-rate was developed, and numerical predictions were obtained by a computer model. A comparison between the experimentally monitored and numerically predicted mass flow-rates showed a very good agreement.

A Second Law Approach to Characterising Thermally Stratified Hot Water Storage With Application to Solar Water Heaters

This paper presents a method of characterising and evaluating the performance of hot water storage systems in terms of their temperature distribution. The change in exergy from the stratified state to the delivery state depends on the stored energy and the stratification. It can thus he used to define the storage efficiency for sensible heat storage devices. A new parameter that isolates the stratification component of the exergy is defined and called the stratification efficiency. The effect of temperature distribution, delivery temperature and tank cross-section on exergy and stratification efficiency is investigated. The advantage that stratification offers over a mixed tank is examined in terms of the storage efficiency and overall solar water heating system performance. Exergy is used to assess the operation of mantle heat exchangers in solar water heating systems and it is shown that exergy and stratification efficiency, as well as energy, should be used to ascertain the performance of such heat exchangers.

Some aspects concerning modelling the flow and heat transfer in horizontal mantle heat exchangers in solar water heaters

An experimental and numerical investigation has been undertaken to study the heat transfer process in horizontal mantle heat exchangers used in solar water heaters. A rectangular cavity has been used as a simplified geometry. With the aid of particle image velocimetry (PIV) the flow field in the centre-plane of the rectangular cavity has been visualized. Three-dimensional flow simulations were performed using a commercial CFD package. The impinging jet formed by the inlet flow directed towards the opposite wall was found to produce localised turbulence in the cavity, with an inlet Reynolds number as low as 360. This turbulence was found to effect the flow field and heat transfer in the cavity when the inlet Reynolds number was above 1200. It is shown that, with the boundary conditions used in this study, most of the heat transferred was in the bottom half of the cavity. This is not the ideal situation for optimization of solar water heating systems. Copyright © 1999 John Wiley & Sons, Ltd.

Mantle heat exchangers for horizontal tank thermosyphon solar water heaters

This paper describes the characteristics of horizontal mantle heat exchangers for application in thermosyphon solar water heaters. A new correlation for heat transfer in horizontal mantle heat exchangers with bottom entry and exit ports was used to predict the overall heat transfer and stratification conditions in horizontal tanks with mantle heat exchangers. The model of a mantle heat exchanger tank was combined with the thermosyphon solar collector loop model in TRNSYS to develop a model of a thermosyphon solar water heater with collector loop heat exchanger. Predictions of stratification conditions in a horizontal mantle tank are compared with transient charging tests in a laboratory test rig. Predictions of daily energy gain in solar preheaters and in systems with in-tank auxiliary boosters are compared with extensive outdoor measurements and the model is found to give reliable results for both daily and long-term performance analysis.

Characteristics Of Vertical Mantle Heat Exchangers For Solar Water Heaters

The flow structure in vertical mantle heat exchangers was investigated using a full-scale tank designed to facilitate flow visualisation. The flow structure and velocities in the mantle were measured using a particle Image Velocimetry (PIV) system. A CFD simulation model of vertical mantle heat exchangers was also developed for detailed evaluation of the heat flux distribution over the mantle surface. Both the experimental and simulation results indicate that distribution of the flow around the mantle gap is governed by buoyancy driven recirculation in the mantle. The operation of the mantle was evaluated for both high and low temperature input flows.

Analysis of horizontal mantle heat exchangers in solar water heating systems

The characteristics of horizontal mantle heat exchangers are investigated for application in thermosyphon solar water heaters. An experimental model of a horizontal mantle heat exchanger was used to evaluate the flow patterns in the annular passageways and the heat transfer into the inner tank. Flow visualisation was used to investigate the flow structure, and the heat transfer was measured for isothermal inner tank conditions. A numerical model of the flow and heat transfer in the annular passageway was developed and used to evaluate the heat flux distribution over the surface of the inner tank. The numerical results indicate that configurations of mantle heat exchangers used in current solar water heater applications degrade thermal stratification in the inner tank. The effects of inlet flow rate, temperature and connecting port location are quantified.